This invention relates to an interior permanent magnet synchronous motor wherein a rotor core has a plurality of permanent magnets incorporated or embedded therein and includes magnetic salient pole sections defined between each adjacent two of the permanent magnets adjacent, and more particularly to a permanent magnet-equipped synchronous motor utilizing both reluctance generated due to the salient pole sections of the rotor core and torque by the permanent magnets.
One of conventional synchronous motors each having permanent magnets incorporated therein is disclosed in Japanese Patent Application Laid-Open Publication No. 18328/1999. The conventional synchronous motor disclosed is so constructed that a width of a core between magnetic poles of permanent magnets is set so as to establish relationship represented by the following expression, to thereby restrain generation of cogging torque:
xcex8minxe2x89xa6xcex8xe2x89xa6maxxcex8max
wherein xcex8 is an open angle of the core of the magnetic poles of the permanent magnets, xcex8 min is a minimum value of an angle defined by two straight lines obtained by connecting distal ends of two end surfaces maximumly spaced from each other of plural end surfaces of teeth corresponding to the width of the core and a center of a revolving shaft to each other, and xcex8 max is a maximum value of an angle between two straight lines defined by connecting two ends maximumly spaced from each other of plural ends of teeth heads of the teeth corresponding to the width of the core and the center of the revolving shaft to each other.
Another conventional synchronous motor wherein a core between magnetic poles of permanent magnets is provided with magnetic salient pole sections is disclosed in Japanese Patent Application Laid-Open Publication No. 205499/1996. The synchronous motor is constructed in such a manner that rotation of a rotor is limited to only one direction, to thereby displace the salient pole sections, resulting in restraining generation of torque pulsation.
In the former synchronous motor disclosed in Japanese Patent Application Laid-Open Publication No. 18328/1999, the open angle xcex8 is defined to be within a range of xcex8minxe2x89xa6xcex8xe2x89xa6max determined depending on the number of teeth, a configuration thereof and a size thereof. However, a timing at which torque is generated between the magnetic poles of the permanent magnets is varied depending on xe2x80x9cthe number of slots per pole and per phasexe2x80x9d q of a stator, so that the synchronous motor fails to satisfactorily restrain cogging torque and torque pulsation.
In the latter synchronous motor disclosed in Japanese Patent Application Laid-Open Publication No. 205499/1996, it is required to displace the salient pole sections of the magnetic poles of the permanent magnets in a direction determined by the direction of rotation of the rotor. This causes the rotor to fail to freely repeat normal rotation and reverse rotation, resulting in failing to sufficiently restrain torque pulsation.
The present invention has been made in view of the foregoing disadvantage of the prior art.
Accordingly, it is an object of the present invention to provide a permanent magnet-equipped synchronous motor which is capable of sufficiently restraining both cogging torque and torque pulsation during feeding of electricity thereto.
In accordance with the present invention, a permanent magnet-equipped synchronous motor is provided. The permanent magnet-equipped synchronous motor includes a stator including a stator core provided with a plurality of magnetic pole sections having windings of at least one phase wound thereon, as well as a rotor of which the number of pole pairs is p (p: a positive integer of 1 or more). The rotor includes a shaft and a rotor core fixed on the shaft. The rotor core has a plurality of permanent magnets incorporated therein in a manner to be spaced from each other at intervals in a peripheral direction thereof. The permanent magnets each constitute a permanent magnet magnetic pole section formed on an outer periphery of the rotor core The rotor is formed with a plurality of magnetic salient pole sections so as to interpose the permanent magnet magnetic pole sections therebetween. The rotor core includes outer peripheral surface sections each positioned between each adjacent two of the magnetic salient pole sections. The magnetic poles of the stator core each include a magnetic pole surface. Each of the outer peripheral surface sections of the rotor core and the magnetic pole surface of each of the magnetic poles of the stator core are arranged so as to have a gap defined therebetween and having a size xcex4d which satisfies the following expression:
xcex4d=xcex4d0/cos(pxcex8d)
wherein xcex4d0 is a size of the gap which is determined along a virtual center line defined so as to extend through centers of two virtual lines extending from a center of the shaft through both ends of the outer peripheral surface section defined in a peripheral direction thereof and xcex8d is an angle between the virtual central line and each of the virtual lines.
The outer peripheral surface sections of the rotor core each may have a contour formed into an arcuate or elliptic configuration. In this instance as well, the arcuate or elliptic configuration may be so determined that a size of the gap has a value approaching to the value determined by the above-described expression.
The gap satisfying the above-described expression constitutes a so-called cosec gap. Such a gap configuration permits a distribution of density of a magnetic flux from the permanent magnets in the gap to approach a sinusoidal wave irrespective of a direction of rotation of the motor, to thereby restrain cogging torque.
The stator core may be so configured that when xe2x80x9cthe number of slots per pole and per phasexe2x80x9d q of the stator core is an integer of 1 or more, an open angle xcex1 of the magnetic salient pole sections which is defined as an angle between two virtual lines defined so as to extend through a center of the shaft and both ends of each of the magnetic salient pole sections in a peripheral direction thereof is defined so as to satisfy an expression xcex1≈nxc2x7xcfx84s wherein n is a natural number and xcfx84s is a slot pitch of the stator core. xe2x80x9cThe number of slots per pole and per phasexe2x80x9d q may be found by an expression q=Ns/(2xc3x97pxc3x97m) wherein Ns is the number of slots, p is the number of pole pairs and m is the number of phases.
Also, the stator core may be so configured that when xe2x80x9cthe number of slots per pole and per phasexe2x80x9d q of the stator core is a fraction of 1 or more, an open angle xcex1 of the magnetic salient pole sections which is defined as an angle between two virtual lines defined so as to extend through a center of the shaft and both ends of each of the magnetic salient pole sections in a peripheral direction thereof is defined so as to satisfy an expression xcex1≈(n/2)xcfx84s wherein n is a natural number and xcfx84s is a slot pitch of the stator core.
Also, an angle xcfx86p between two virtual lines extending from a center of the shaft through both ends of each of the outer peripheral surface sections and an open angle xcex1 of the magnetic salient pole sections which is defined as an angle between two virtual lines extending through the center of the shaft and both ends of each of the magnetic salient pole sections in a peripheral direction thereof are defined so as to satisfy an expression (180/p+xcex1xe2x88x92xcfx86p)/xcfx84s≈2nxe2x88x921 wherein xcfx84s is a slot pitch of the stator core, n is a natural number, xcex1 greater than 0, xcfx86p  greater than 0, and xcex1+xcfx86pxe2x89xa6180/p.
In a motor wherein the gap does riot constitute a so-called cosec gap as well, torque pulsation may be satisfactorily restrained by setting the angles xcex1 and xcfx86p so as to permit the relationship described above to be established.